1. Field of the Invention
The present invention relates to a tilt device for a machine tool.
2. Description of the Related Art
A tilt device is known that includes a tilt member provided so as to be swingable and a drive motor that provides a drive force for swinging the tilt member. Such a tilt device is provided to a machine tool. The machine tool inclines a workpiece or a tool disposed on the tilt member to index the workpiece or the tool to perform predetermined machining.
When the tilt member is inclined with respect to a balanced position, the tilt member is subjected to a moment that urges the tilt member back to the balanced position using the gravitational force (hereinafter referred to as an “unbalance moment”). The unbalance moment generated in the tilt member becomes larger as the inclination angle of the tilt member becomes larger, and serves as a load applied to the drive motor which operates to maintain the tilt member in the inclined state. Thus, it is necessary to use a large drive motor in the case where the weight of the tilt member and the workpiece or the like to be disposed on the tilt member is heavy and it is attempted to support the load applied to the drive motor by the unbalance moment using only the drive torque from the drive motor.
Japanese Patent Application Publication No. 2010-167508 (JP 2010-167508 A) discloses a technique of alleviating a load applied to a drive motor by coupling a cylinder device to a tilt member and canceling out an unbalance moment using an urging force provided from the cylinder device to the tilt member.
In JP 2010-167508 A, when the inclination angle of the tilt member becomes less than a predetermined inclination angle, the moment provided from the cylinder device to the tilt member becomes more than the unbalance moment generated in the tilt member. That is, the direction of the load applied to the drive motor is inverted, and the direction of drive torque from the drive motor is also inverted, depending on whether the inclination angle of the tilt member is larger or smaller than the predetermined inclination angle. Thus, in the course of swinging the tilt member, a backlash may be caused in the tilt member because of the inversion of the drive torque from the drive motor when the inclination angle of the tilt member exceeds the predetermined inclination angle.